The present disclosure is related to methods for producing catalyst compositions from precursors containing both volatile and non-volatile components, and the compositions obtained therefrom.
Exhaust emission control devices (e.g., catalytic converters, NOx catalysts, selective catalytic reduction catalysts (SCR), and so forth) utilized in exhaust systems of vehicles generally comprise a housing around a ceramic, metallic-honeycomb or corrugated substrate coated with a catalytically active layer. The catalytically active layer, which generally comprises high surface area porous particles, promotors, stabilizers, binders, and catalytically active precious metals, is preferably applied to the substrate in the form of a wet slurry (e.g., a washcoat) so as to uniformly coat the interior walls of the substrate. The coated substrate is then calcined in a gas fired or electric oven/furnace in order to remove water and other volatile compounds such as, for example, alcohols (e.g., methanol, ethanol, and the like,) acetone, toluene, and the like, nitric oxides, sulfurous oxides, and the like, from the coating.
The calcining of catalyst compositions solely via convection or conduction equipment, such as, for example, gas fired or electric ovens, is time-consuming and expensive, with calcining temperatures generally being around 500° C., and calcining times generally being about 3 to about 7 hours or so. In addition, these methods of calcining embody poor energy transfer to the catalyst, which leads to: non-uniform heating of the catalyst, uneven water evaporation from the washcoat, formation of chemical concentration gradients within the washcoat, and severe thermal shock for certain types of substrates that can result in the fracture of the substrate.
As a result of these drawbacks, there remains a need for methods of producing catalyzed substrates with more even heating across the bulk of the catalyst and/or with reduced production cycle times and hence reduced production costs.